Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare this as a non-read-only, open-world, non-idempotent write. The description goes beyond them by disclosing the log-vs-timer branching, that start defaults to now, and that required custom fields can cause refusal — useful failure-mode context. It omits auth requirements and the single-running-timer constraint.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loads the 'WRITE' marker, then two compact sentences covering mode, default, precondition, and endpoint. Every clause earns its place with no padding.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a nine-parameter write tool with no output schema and zero required params, the description covers mode selection, defaults, and the main refusal case. It could say more about the return value or running-timer conflicts, but the essentials are present.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the baseline is 3. The description restates the end-omitted/start-default behavior that the schema properties already document, adding only the cross-parameter interaction. Little net new meaning.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('add a time entry for yourself') and disambiguates the two modes: with end it logs completed time, without end it starts a running timer. This cleanly separates it from siblings like clockify_stop_timer and clockify_update_time_entry.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives clear mode-selection guidance (supply end to log, omit it to start a timer) plus a failure precondition about workspaces with required custom fields. It stops short of naming alternatives such as stop_timer or update_time_entry, or warning that an already-running timer may block a new one.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.